In a manufacturing process of a semiconductor device or an LCD substrate, an etching process is performed to form a pattern of a thin film. As one of a variety of etching apparatuses, for example, there is a parallel plate plasma etching apparatus, wherein parallel plate electrodes including a pair of an upper and a lower electrode are disposed in a chamber, and a high frequency electric field is formed therebetween by applying a high frequency power to either one of the electrodes while introducing a processing gas into the chamber. Due to the high frequency electric field, a plasma of the processing gas is generated, whereby an etching process is performed on, e.g., a semiconductor wafer (hereinafter, referred to as a “wafer”) W.
For example, in the semiconductor device, a low dielectric film (low-k film) is practically used or tested as an interlayer insulating film, a gate insulating film or the like. As the low dielectric film including silicon (Si) and oxygen (O), for example, there are an SiOC film formed by adding carbon to an SiO film serving as a base film and an SiOCH film formed by adding carbon and hydrogen onto the SiO film. When etching those films, a gas containing carbon (C) and halogen such as fluorine (F), chlorine (Cl) and bromine (Br) is used as a processing gas.
In etching, a hole (recess) is formed by an etching action of an etchant together with polymerization which forms polymer on a sidewall of the hole to protect the sidewall. For example, when the SiO-based film is etched by using a gas containing carbon and fluorine (hereinafter, referred to as a “CF-based gas”) as a processing gas, active species of CF, which are produced when the CF-based gas is converted into a plasma, cause both the etching and the polymerization.
The CF-based gases such as CF4 gas, CHF3 gas, C2F6 gas, C3F8 gas, C4F8 gas, C4F6 gas, and C5F8 gas have different etching action and polymerization. Therefore, although etching target films are the same, the most suitable kind of gas is selected from the CF-based gases depending on a film thickness ratio of the etching target film to an underlying film or a resist film.
Further, in the conventional parallel plate plasma etching apparatus, in order to improve uniformity of etching characteristics (e.g., an etching rate and processing dimensions after etching) on the surface of the wafer W, the processing gas is supplied toward the wafer W from the upper electrode configured as a shower head having a plurality of gas injection openings, for instance, while varying gas flow rates supplied onto a center part and a periphery part of the wafer W.
However, due to lack of a consistent and reliable method for determining a flow rate ratio of gases supplied to the central and the periphery part for respective CF-based gases, the flow rate ratio is determined through many trials and errors to perform an etching process with a high in-surface uniformity. Thus, a lot of efforts and time are necessary to determine the flow rate ratio.
Japanese Patent Laid-open Application No. 2002-184764 discloses a technology wherein when an etching process is performed on TEOS and a resist by using a gaseous mixture including C5F8 gas, gaseous mixtures having different flow rate ratios are supplied from two gas injection openings of the shower head which are concentrically formed such that an oxygen flow rate is lower in the periphery part, thereby preventing an etching selectivity (TEOS/resist) in the periphery part from being deteriorated. Even in the aforementioned patent document, however, there is not disclosed a consistent and reliable method for determining a flow rate ratio of gases supplied to the central and the periphery part of the wafer W when an etching is performed by using the CF-based gas.